Measuring the parameters associated with solid-fluid flow systems has been interesting to researchers in areas such as pneumatic solids transport, slurry flow, air quality monitoring, and most recently, fluidized-bed combustion and gasification. Many different fundamental principles have been applied in attempts to provide one or more measures of parameters associated with the dynamic behavior of gas-solids flows.
Stukel and Soo (1969) used isokinetic samplings of a 10-micrometer (.mu.m) magnesia particle-air mixture to determine local mass flow (.rho.v) and a fiber optic probe to measure the local particle density (.rho.). They used the ratio of these two quantities to give the value of the local particle velocity (v).
The studies of Gillespie and Gunter (1959) indicate that entrained particles as large as 50 to 400 .mu.m have little effect on the air-particle flow pattern. This suggests that the mean force, exerted on a surface placed normal to the direction of flow, could be used as a measure of dust concentration and that a solids pressure device based on this principle should be feasible. Mann and Crosby (1977) determined the local flow characteristics of coarse particles in pneumatic conveyors by using a piezeoelectric transducer. The parameters measured include local particle flow rate, local average particle velocity and local velocity distribution.
Birchenough and Mason (1976) used a laser anemometer, based on the Doppler effect, to obtain particle axial velocity profiles in two-phase, gas-solid flows. The system was intended for use in those instances where the flow stream had a particle concentration low enough for laser penetration through the volume to be monitored.
Irons and Chang (1983) used capacitance measurements between electrodes mounted on the surface of a flow-containing pipe to measure average void fractions and particle velocities with errors believed to be less than eight percent. Smith and Klinzing (1986) used another electrically based approach. They recorded the current flow to two electrodes, which were separated by a known distance along the direction of flow. The two current values were produced by the loss of the frictionally generated charge on the entrained particles upon collision with the electrodes. The two-electrode current data were processed using cross-correlation techniques to obtain a measure of the average particle velocity.
A one-axis impact probe using strain-gauge-based particle detection was developed by Raso, Tirabasso, and Donsi (1983). In this device, the strain gauge senses impacts imparted to a thin, hollow rod probe. The probe was made smaller for low intrusiveness and provided measures of local particle concentration and velocities in gas streams. The probe was sensitive to the impact of single particles, and its small size allowed its measurement to be good approximations to point values. However, restriction to sensing of particle impact along a single axis limits the amount of data obtainable with such a probe device. Desired features for an improved measuring device include a capability for measuring or deriving particle impact momentum vectors along three axes so as to enable generation of better data bases and for determining solid pressure gradients within a cold fluidized bed. Such data is fundamental to mechanistic mathematical models for fluidized bed particle dynamics prediction.